Method and apparatus for controlling the effect of the centrifugal force on the stock in pulp defibrating apparatus

In the method of refining pulp stock in which the pulp to be ground is introduced into a grinding space including a first grinding zone defined between opposing grinding discs having ridges and grooves providing grinding surfaces, which discs are carried by a pair of rotatable discs which rotate relative to each other in an environment of fluid medium under superatmospheric pressure and correspondingly elevated temperature in a housing, and in which first grinding zone the pulp material is accelerated outwardly by the centrifugal force generated by the rotational movement of the rotatable discs,

• the improvement for controlling the effect of the centrifugal force on the pulp comprising the step of:
• providing a second grinding zone extending angularly from said first grinding zone for receiving the pulp accelerated through said first grinding zone and changing its direction of flow, said second grinding zone being defined between one of said rotatable discs and a stationary grinding surface on at least a portion of the surface of a stationary element mounted within said housing, the angle of said second grinding zone relative to said first grinding zone being calculated to split the centrifugal force exerted on the pulp material in said second grinding zone into two different force vectors to thereby reduce the accelerating force on the pulp in said second grinding zone to prolong the dwell time of said pulp in said grinding space.

In a pulp defibrating apparatus in which the pulp material to be ground is introduced into a grinding space including a first grinding zone defined between opposing grinding discs having ridges and grooves providing grinding surfaces, which discs are carried by a pair of rotatable grinding discs which rotate relative to each other in an environment of fluid medium under superatmospheric pressure and correspondingly elevated temperature in a housing, and in which first grinding zone the pulp material is accelerated outwardly by centrifugal force generated by the rotational movement of the rotatable discs,

• the improvement for controlling the effect of centrifugal force on the pulp comprising:
• a stationary element having a stationary grinding surface defined thereon, said stationary element being mounted in said housing with said stationary grinding surface being opposed to said grinding surface of one of said rotatable discs for defining a second grinding zone therebetween, said stationary element and said one of said rotatable discs being so configured and positioned that said second grinding zone defined therebetween extends from the outer end of said first grinding zone for receiving the pulp therefrom and that said second grinding zone is angled relative to said first grinding zone for causing said pulp to change its direction of flow upon entering said second grinding zone, the angle of said second grinding zone relative to said first grinding zone being calculated to split the centrifugal force exerted on the pulp material in said second grinding zone into two different force vectors to thereby reduce the accelerating force on the pulp in said second grinding zone to prolong the dwell time of said pulp in said grinding space.